Aerofoils, such as those used in aircraft, commonly comprise leading or trailing edge structures. These structures are arranged to modify the shape of the aerofoil to enable the aerodynamic lift of the aerofoil to be modified. Primarily, the lift is modified so as to reduce the stall speed of the aerofoil during take-off or landing of an aircraft.
Leading edge structures commonly comprise a fixed part, fixed to the wing box, and a movable part, hinged on the fixed part. Actuators are arranged to move the movable part between a stowed position, in which the lift of the aerofoil is suitable for aircraft flight at cruising speeds, and a deployed position in which the aerofoil lift is increased for the lower speeds of takeoff or landing.
In some leading edge structures, such as droop noses, the stowed moveable part provides the leading edge surface for the aerofoil. The stowed movable part sits forward of the fixed part which itself has a leading edge surface that is at least partly covered by the stowed movable part. In its deployed position, the movable part hinges downwards and exposes the covered section of the leading edge surface of the fixed part.
The movable leading edge structure itself has a trailing edge, which borders the leading edge surface of the fixed part. There are a number of problems relating to this area of the leading edge structure. For example, when the movable part is deployed, its trailing edge can lift due to the aerodynamic pressure differential on the aerofoil. Such lifting may cause air to be forced between the movable and fixed parts of the leading edge structure, thus reducing the efficiency of the aerofoil by increasing drag. In order to reduce this problem, the trailing edge is biased against the exposable leading edge of the fixed part. However, this biasing can result in significant wear between the movable part trailing edge and the exposable leading edge surface of the fixed part. Another problem with this structure is the shape of the exposable leading edge surface of the fixed part has to be profiled to accommodate the position of the trailing edge of the movable part as it moves between the stowed and deployed positions. Thus the profile of the exposable leading edge surface may not be optimal. Furthermore, the transition between the trailing edge of the deployed movable part and the exposed leading edge surface of the fixed part may be not be aerodynamically optimal.